Frequency Sensitivity Analysis of Coil-IDE Resonance Topology Circuit and Its Humidity Sensor Applications

In this article, the frequency sensitivity of the Coil-interdigital electrode (IDE) sensor in different integrated topologies is studied. In particular, the expression of the resonance frequency of the Coil-IDE sensor both in series and parallel topological structure is derived. The sensitivity of frequency to IDE capacitance was analyzed, and two new results can be found 1) due to the existence of coil winding capacitance and grounding capacitance, the Coil-IDE topology circuit has been changed, which causes the Coil-IDE parallel topology structure has a higher frequency sensitivity than series and 2) not only the topology structure but also the parameters such as coil inductance and IDE capacitance have the regulatory effect on the frequency sensitivity. After analysis, an experiment of a Coil-IDE humidity sensor was applied to verify the presented results. The parallel frequency of the Coil-IDE parallel structure having a higher sensitivity was confirmed. The error of the proposed formula predicting the regulatory effect of parameters on frequency sensitivity was discussed. The error is as low as 7.57%, which shows the beneficial aspect of the integrated design of Coil-IDE sensor both in topological structure and parameters.